ADD ON:
I thought I better add to my post that the rocks are chunks of beautiful sparkly pink granite, so not that porous (?) and worth cleaning up...

I would guess that RoundUp would be the most commonly used herbicide and you can get rid of it with a soak in a mild ammonia solution. Bleach is less effective for RoundUp.

Of course, you will need to rinse and soak again in clean water. Allow to dry in the sunlight for several days, if you can.

Thank you Rhizo! I was told to hurry and take all the ones I wanted, and didn't want to haul a ton of rock that were not good for anything... Covered with weed killer, I would have been afraid to even put them in my garden. My husband suggested after I "wash them" I could pile them in a corner of the yard and let them weather awhile. Someone else suggested after I cleaned them, try them in a tank with a few "feeder fish" to make sure nothing is leeching out of them. Sounds a bit cruel...but....

You should try posting this in the Aquarium forum. Although it seems like they tell you not even to use soap on anything that goes inta an aquarium. Seems a little extreme, but I don't really know.

WW